Acyl isethionate salts have been utilized for many years as surfactants in body care compositions. They are generally used in combars or synthetic detergent bars where their increased mildness in relationship to soaps are an advantage. The stability of these compositions under aging conditions such as shelf life have been studied for some time. Various antioxidants have been placed into soap and acyl isethionate compositions in order to provide increased stability under shelf life conditions. Various references are known which discuss the utilization of antioxidants to enhance shelf stability. Some of these antioxidants are known free radical scavengers which stop deterioration causing reactions from occurring. Examples of such antioxidants are butylated hydroxy toluene, (BHT) and butylated hydroxy anisole (BHA). Additionally it is well known that certain metals catalyse reactions which bring about the deterioration of the bar. Examples of such metals include iron and copper. Various chelating agents have been utilized to remove the metallic ions from interacting as a catalyst for the deterioration causing reactions. Examples of such materials include ethylene diamine tetra acetic acid (EDTA) or a soluble salt thereof such as a tetrasodium salt. A further chelating agent is 1-hydroxy ethane-1,1-diphosphonic acid (EHDP) or a soluble salt thereof.
It is known to add such agents to acyl isethionate containing personal care compositions to improve their storage properties, for example see UK 1169551 issued to Unilever.
A recent Unilever patent issued by the European Patent Office subject to opposition, EP249474B1, has investigated the shelf stability-deterioration reactions of acyl isethionate further. It has made a study of the usage of the various antioxidants i.e. the 2,6 di-t-butyl-4-hydroxy toluene, previously referred to as BHT, as well as the usage of chelating agents in acyl isethionate containing compositions. At the bottom of page 2 of the published specification is the following paragraph:
A preferred sequestering agent for copper is ethylene diamine tetra acetic acid (EDTA) or a soluble salt thereof such as its tetra sodium salt or mixtures thereof. Such agents are known to enhance the activities of iron in accelerating autoxidation, however it can be used successfully provided there is a satisfactory sequestering agent for iron present. The two sequestering agents are then acting synergistically. PA1 a. about 5 to 85 wt % of an acyl isethionate salt. PA1 b. about 90 to 5 wt % of soap, and PA1 c. an effective amount of a metal chelating agent consisting solely of an agent selected from the group consisting of ethylene diamine tetra acetic acid, water soluble salts of ethylene diamine tetracetic acid, or mixtures thereof, said composition have a pH of from about 7.2 to 10.
Therefore even though EDTA is known to be a chelating agent in general for various metallic ions, its use alone in acyl isethionate compositions is cautioned against because it accelerates autoxidation; one of the important reactions which brings about deterioration of a detergent composition and, interalia, a bad odor.
It has now been surprisingly found in view of this statement in EP249474 that EDTA and/or its soluble salts can be utilized successfully in acyl isethionate containing compositions of a certain nature. Thus, the usage of additional chelating agents is unnecessary. The usuage of only EDTA and/or its soluble salts brings about a stable composition.